Regulation of gonadotropin-releasing hormone receptors by protein kinase C: inside out signalling and evidence for multiple active conformations

Christopher J Caunt, James N Hislop, Eamonn Kelly, Anne-Lise Matharu, Lisa D Green, Kathleen R Sedgley, Ann R Finch, Craig A McArdle

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

Desensitization and internalization of G protein-coupled receptors can be mediated by phosphorylation within the C-terminal tail, facilitating beta-arrestin binding and targeting the receptor for internalization. Type II GnRH receptors (GnRH-Rs) show such regulation, but type I GnRH-Rs lack C-tails and are not rapidly desensitized or internalized. Here we show contrasting susceptibility of type I (human and sheep) and II (Xenopus) GnRH-Rs to regulation by protein kinase C (PKC). When human (h) or Xenopus (X) GnRH-Rs were expressed using recombinant adenovirus, PKC activation increased radioligand binding to XGnRH-Rs but not to hGnRH-Rs. A dominant-negative dynamin mutant (K44A) inhibited internalization of XGnRH-Rs (but not hGnRH-Rs) without influencing PKC regulation of XGnRH-R binding. PKC activation increased the affinity of XGnRH-Rs for the type II GnRH ligand and increased effects of low concentrations of GnRH-II on the [Ca(2+)](i) but had no effect on type I ligand binding to hGnRH-Rs, sGnRH-Rs or XGnRH-Rs, or to chimeric receptors with the XGnRH-R C-tail added to a type I receptor. Binding of type II ligand to human or sheep receptors was also unaffected but was increased in the chimeras. Mutation of both PKC-phosphorylation consensus sites in the XGnRH-R tail did not prevent the PKC-mediated increases in binding or alter agonist-induced translocation of beta-arrestin2/green fluorescent protein or inhibition of inositol phosphate accumulation by beta-arrestin2/green fluorescent protein. Thus, it appears that there are two distinct active conformations of XGnRH-Rs (differing in affinity for type I and II ligands) and that these cells exhibit a novel form of inside-out signaling in which PKC feeds back to influence receptor affinity.
Original languageEnglish
Pages (from-to)3594-602
Number of pages9
JournalEndocrinology
Volume145
Issue number8
DOIs
Publication statusPublished - Aug 2004

Keywords

  • Binding Sites
  • Gonadotropin-Releasing Hormone
  • HeLa Cells
  • Humans
  • Phosphorylation
  • Protein Conformation
  • Protein Kinase C
  • Receptors, LHRH
  • Signal Transduction
  • Tetradecanoylphorbol Acetate

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